It is a well known fact, particularly when rice grains are to be husked, polished and whitened, that rice mills are generally designed such that breakage of the grain is avoided as much as possible, particularly in the stages of husking and of polishing and whitening the grain.
For the purpose of husking, as well as polishing and whitening cereal grains, particularly rice, many different types of machines are very well known in the art, all of them working in separate stages, namely, a husking stage and a polishing and whitening stage. It is also well known that the husking machines must deliver completely husked grain to the polishing and whitening machines, because the latter are uncapable of handling unhusked grains, whereby the husking stage generally needs several steps carried out by tandems of husking machines and/or by husking machines followed by unhusked grain removing machines.
Different designs of whitening and polishing machines are well known but, up to the present time, no machine has been designed that may effect a complementary husking of the grain to avoid the use of unhusked grain removing machines, as well as the polishing and whitening thereof in one single step, with the consequent increases in the cost of fully husking the grains and the consequent cumbersome procedure that must be used with said type of tandem husking machines and unhusked grain removing machines to deliver a fully husked grain to the polishing and whitening machines.
Among the most well known grain polishing and whitening machines are those using emery cones or emery cylinders to polish and whiten the grains by means of rubbing of the same with emery, producing a polished grain and flour from the rubbed portions thereof, but these machines are extremely bulky and heavy and their operation requires high power consumption, whereby the process carried out in the same is rather costly.
Also polishing and whitening machines for horizontal operation and machines for vertical operation are well known, but in machines designed for horizontal operation, grain elevators are required which are of rather intricate construction and increase the cost of installation of such machines.
In rice mills using horizontally arranged polishing machines, in order to avoid the high cost of elevators for grain, said machines are mounted in a cascade arrangement, that is, are mounted at different successive levels, whereby the installation of stairways and the like for inspection and repair purposes is required, which absorbs a greater space and involves a rather slower and intricate operation.
Compact type horizontal polishing and whitening machines for rice are also known, but these compact type machines use a rotor the rotation of which causes intermittent projection of the grains that therefore are accelerated or deccelerated, depending on the cycle involved, whereby the treating of the grain is harsh and irregular and a large amount of breakage of said grain occurs.
Most of the well known whitening and polishing machines for cereal grains, particularly for rice, generally use a cylindrical rotor and a polygonal indented screen, because it was believed up to the present time that the use of such polygonal indented screen would increase the performance of the apparatus, because the building up of a mass of grains in the corners of the polygonal screen would produce rotation between the different layers of grain and thus an energetic rubbing of the grains against each other, which supposedly would aid to the polishing of the grain in a more efficient manner. However, it has now been discovered that there is no reason whatsoever for maintaining the polygonal, particularly hexagonal shape of indented screens, because the said screens used in most of the prior art polishing or pearling machines for grains, do not perform as previously thought, and rather produce heavy accumulations of grains in the corners of the hexagonal screen, which grains are kept there without any treatment whatsoever.
The screen type machines of the prior art, on the other hand, generally use indentations in the screens that interfere with the slots of the screen, thereby forming extremely sharp protruding edges that materially form sharp knives that, rather than polishing the grain, cut the surface thereof and many times cut through the bodies of said grains with the consequent breakage and the obvious dissatisfactory uniformity of the polishing action achieved thereby.
Most of the above described drawbacks shown by all the prior art polishing or whitening machines for rice, have been appropriately solved by the whitening and polishing machine of U.S. Pat. No. 3,960,068 to Felipe Salete, the same applicant of the instant application. Said patent discloses a whitening and polishing machine essentially comprising a housing, a hollow rotor within said housing, feed means to admit grain into the housing, a screw conveyor at the lower part of said rotor for conveying the grains upwardly into the treating section of the machine which is arranged at the upper part of said rotor, a cylindrical indented screen in said treating section and a rotor having a pair of knives to retain the movement of the grains at will, whereby the pressure applied by said screw conveyor upwardly of the machine, pushes the grains to be trapped by said rotor which spins the mass of grains against the action of the indented screen, thus rubbing the grains one to each other and against the walls of the rotor and the walls of the indented screen, to thereby whiten and polish the same. The flour which is removed from the grains, is entrained in a stream of air which is forced through the hollow rotor and outwardly thereof through suitable bores, in order to cross the mass of spinning grains and the screen, so that said flour is taken out from the treating chamber of the machine and downwardly falls by gravity in order to be collected in an appropriate receptable. The treated grains in turn are pushed upwardly against a centrifugal extractor, which expels the same outwardly of the machine. The machine U.S. Pat. No. 3,960,068, while highly efficient and extremely economic in its operation, still presents some drawbacks, among which the following may be mentioned. The machine of U.S. Pat. No. 3,960,068 does not solve the problem extant in practically all rice mills, namely, that if the rice is not properly husked in the husking machines, an additional husking operation and/or unhusked grain removing operation is required in the husking stage, because the machine of U.S. Pat. No. 3,960.068 is absolutely unable to husk the unhusked grains received.
The machine of U.S. Pat. No. 3,960,068, on the other hand, may only be arranged in a vertical position, which reduces its versatility because there are many rice mills that require horizontal arrangement of polishing machines. Also, said machine is not capable of orienting either the feed means or the discharge means for grain, whereby the grains must be always fed in the same position and always discharged in the same position, respectively.
Said machine also lacks means to orient the position of the individual spinning grains, whereby some times the rotor or the indented screen traps the grains in a transverse position, producing serious breakage thereof and the percentage of said breakage may at times be relatively high, with the consequent uneconomical results.
It is therefore very well known that all the workers in the cereal grains husking, polishing and whitening field have long sought a machine that may be able to overcome the above described drawbacks and particularly a machine that may perform, in one single step, both the husking operation of the grains that were not completely husked by the husking machines, and the whitening and polishing thereof, in order to solve the very serious problem extant up to the present time in all prior art rice mills, namely, that the husking machines generally do not perform with 100% efficiency, whereby many individual grains are expelled from said machines with all or part of the husk covering them, thus requiring a further husking stage or an unhusked grain removing stage, because the prior art polishing and whitening machines were unable to treat the unhusked grains that were fed into the same. A machine which may solve the problem of husking the unhusked grains coming from the husking operation at the same time that it polishes and whitens the same, represents a breakthrough in the art and, therefore, such machine has been long sought, without any success up to the present time.